Use any stock that is safe for your needs. Homemade tastes bests, but canned works just fine.
To make beef flavored, use beef stock and replace poultry seasoning with a pinch of thyme.
Gluten: Gluten is a protein found in specific grains (wheat, spelt, kamut, barley, rye). Other grains are naturally gluten-free but may have cross-contact with gluten-containing grains. Look for certified gluten-free products if you need to avoid gluten. Find out more about wheat and gluten substitutions.